This is one of those ideas for when my 390 gets done. It will have 9.5:1 static compression, a 343941 cam, and TRW L2291F30 pistons. I sent off for some literature on the ATI ProCharger. It is a belt driven centrifugal supercharger. It can be driven off a normal belt, not one of those humongus belts like for the rootes superchargers. Most of their stuff is for 5.0 mustangs, but they do have superchargers for big blocks (probably brand "C"). I was thinking a blow through system with the entire carburetor inside a welded up box. A cable would have to control the throttle.

My question is, would supercharging, with about 8-10 psi of boost, be reasonable for this motor? How much hp do you think I'd make? Can the bottom end, with its stock short rods, and cast crank, handle it? I do have the block with the reinforced main webs.

Thoughts, ideas, dillusions?

 

My hotrod: 64 Galaxie with a 68 390 GMC 6-71. It is a complete STOCK longblock(mild cam .531 lift). Rebuilt rods(bolts/bushings), original pistons, cast crank. I put 6 lbs of boost to it. It by far is not a real screamer, but it does not get left behind. I kinda built it with left over pieces. There is lots of room for major improvements when money comes around.

With "normal" driving it will last forever. Quick blasts aren't going to hurt it unless you lean it out. I had a '96 F350 460FI truck that I put a Vortech supercharger on. It would fly for the beast that it was. It ran 15.8's one time at the track. Back in '97 the Lightnings weren't going much quicker stock. With 9:1 compression I would not push the boost too high. Most blower motors are 7-8:1 static. One think to make sure is FUEL! Make sure it doesn't lean out....things will go BOOM Careful tuning will yield you a flyin' machine

I think the Vortech literature stated 100hp increase on my 460 with 6 lbs of boost. I know the off-idle power went up big time. Boy do I miss that truck.

I know that someone(maybe Vortech) offers a carb BOX that includes all the arrangement to operate the carb:fuel line fittings, sealed internal carb linkage, and a large inlet to hook to blower.

Larry

 

I just got done looking at their carb box. I think I could build (read weld up) one for a lot less than the $800 they're asking for it, although it is one slick looking box.

I think PVC plumbing would be cheap and effective, any thoughts on that?

According to the ATI procharger literature, you can run 8-10 psi of boost with 9:1 compression, so I think 8 psi isnt too much of a longshot with 9.5:1, especially if I intercool it.

Again, this is not going to happen right away, this is more of a long term idea I got in the back of my head...

 

I just found some more info on intercooled centrifugal supercharging. According to this , I can safely run up to 15 psi of boost! Imagine the power...

Now my question. Are FE's more or less prone to detonation (ping) than other engines?

 

I've seen a few people throw a centrifugal blower on their stock motor and then wonder why they're picking their pistons up off the highway.

As long as you have the fuel delivery to handle it, you'll be fine. Just remember the principles of a supercharger. It takes the incoming air and rams it down the intake. If you don't have enough carb, in my opinion at least 950cfm, you risk detonation with any engine.

A supercharger will also increase your compression, so either an o-ringed head gasket or o-ringed heads would be a good idea.

Just remember the golden rule: Horsepower doesn't come cheap.

 

no way can u safely run 15 psi of boost. There would be a lot of power but for how long.

 

They say that becuase it's intercooled, you dont run the risk of detonation that you get with a non-intercooled application, like a roots supercharger. They also say their centrifugal makes a lot less heat to begin with than the roots.

If 302's in mustangs can handle it, I fail to see why a 390, with it's stronger block, couldn't. Keep in mind, I would be running TRW forged pistons.

Read this, and look at the graph about halfway down the page:
http://www.procharger.com/intercooled.shtml

I would be running 9.5:1 compression, and according to the graph, it says about 15 psi reliably. The graph also says, at 9.5:1 with a roots, about 4 psi is the maximum.

 

Fuel is the biggest problem, as mentioned. The strength of the surrounding parts is also a big question.

Cast cranks, stock rods are not going to take the abuse either. Just because the piston will take the heat, does NOT mean the rods are not going to find there way out the side. I have a couple friends running stroker Windsors with big boosts, and they have there share of problems. They do have good parts in the bottom, but head gaskets are a normal wear item. O-ringing helps, but when you play hard it costs.

 

Ok, I'm just trying to get an idea of what it would take. This is not something I would be doing in the near future, something I might do sometime down the road. So maybe a few upgrades should be in order. How about:

Eagle H-beam rods

FT forged steel crank, rebalanced for internal balance

ARP hardware

Although it wont be a problem right now (with no supercharger), how would I get a constant 6psi to the carb, with such varying boost pressures in the carb enclosure?

 

All the above mentioned parts will help make things last. Mine is very stock, so I am very conservative with boost. It's a cruiser for now. Like I mentioned, when the money comes around for a better bottom end, I can then start turning it up.

Not really sure what you mean: constant 6 psi to carb with such varying boost pressures in the carb enclosure??

Boost only occurs under load, near WOT. This all depends on the type of blower you have. The smaller ones will produce quicker boost than a larger Roots type. I saw this with the two vehicles that I have(had). My 96 F350 had a Vortech and it pulled 1-2 lbs boost around town with just mild driving. My 64 6/71 takes more throttle to get boost. With such a large blower, underdriven as much as mine, it takes more to get response.

The boost is relative to the size of the blower and how fast you spin it(along with details of the compression of motor). My 6/71 gets 6 lbs on a cold day, maybe 5 on a hot day. It depends on the air quality. The most you can do is set it up for a "range" and go from there. You will never get a specific reading, with so many variable.

Larry

 

What I mean is, the carb needs about 6-8psi of fuel pressure, constantly. The way it is now, the fuel pump is set to that, and that's what it gets, since atmospheric pressure doesnt change much. But when I enclose the carb, at maximum boost the boost pressure will be more than the fuel pressure, and the carb wont get fuel. I'm looking for a way to regulate it, so that external (outside of the carb box) fuel pressure rises directly proportionally to the boost pressure. This way, the carb would always have the correct pressure.

Edit: It's going to be a blow through system, with the carb in a sealed box. I dont know if this was made clear.

 

mallory has adjustable fuel pressure regulators that will increase fuel pressure as boost increases. but you need a good enough fuel pump (electric) to pull it off

 

Well I have yet to round up the money for intake/drive but i plan on running a stock rod and stock crank with regular trips to 6k with a 6-71 jimmy @ 10 psi And I am not worried.As i keep saying it has alot to do with the balance.All the pistons are within 1 gram.Rods where done to 2 grams. Man is that a pain in the ***,took many hours to get them to match up on the big end.Also detination will kill pistons,so a few gallons of race gas will go in every tank

 

Cool, what engine is that?

 

352 block 428 crank 289/302 pistons